Multipoint thermocouple

ABSTRACT

A multipoint thermocouple for sensing temperature. The thermocouple comprises a sheath having a plurality of conductor pairs disposed within the sheath. Each conductor pair has two conductors of dissimilar materials joined at a unique junction point along the sheath. The unique junction points permit sensing of temperature at different locations along the length of the multipoint thermocouple.

FIELD OF THE INVENTION

[0001] The present invention relates generally to sensing temperature,and particularly to thermocouples designed to sense temperature atmultiple points.

BACKGROUND OF THE INVENTION

[0002] Thermocouples are used in a variety of applications to sensetemperature at a given location. A typical thermocouple comprises anexternal sheath and a pair of rod-shaped conductors disposedlongitudinally within the sheath. Each conductor is of a dissimilarmetallic material, and the two conductors are joined at a distal endwithin the sheath. An electrical insulation material also is packedabout the rods within the sheath. The free ends of the conductors areconnected to a detection instrument, such as a voltmeter, that measuresthe difference in potential created at the junction of the two metals.This difference in potential changes with temperature, thereby readilypermitting the accurate detection of temperature at the junction point.

SUMMARY OF THE INVENTION

[0003] The present invention relates generally to a multipointthermocouple system. One exemplary embodiment of the system comprises asheath. Within the sheath, a plurality of conductor pairs are disposed.Each conductor pair comprises two conductors of dissimilar materialsthat are joined at a junction point. Each pair is designed such that itsjunction point is at a unique longitudinal location along the sheath.Thus, a multipoint thermocouple with a single sheath can be utilized tosense temperature at a plurality of distinct locations. The conductorpairs are electrically separated by an electrical insulation materialdisposed about the conductor pairs within the sheath. The invention alsorelates to a methodology for sensing temperatures at a variety oflocations via a multipoint thermocouple.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] The invention will hereafter be described with reference to theaccompanying drawings, wherein like reference numerals denote likeelements, and:

[0005]FIG. 1 is a side view of an exemplary, multipoint thermocouple,according to one embodiment of the present invention;

[0006]FIG. 2 is a schematic, cross-sectional view of a multipointthermocouple, according to the present invention;

[0007]FIG. 3 is a side view of the thermocouple illustrated in FIG. 1with an end cap of the sheath exploded from the remainder of the sheath;

[0008]FIG. 4 is an end view taken of the exposed conductor pair endsshown in FIG. 3;

[0009]FIG. 5 illustrates an exemplary application of the thermocouple ofFIG. 1;

[0010]FIG. 6 illustrates a high pressure reaction vessel combined with athermocouple, according to an exemplary embodiment of the presentinvention;

[0011]FIG. 7 illustrates an exemplary alternate embodiment of themultipoint thermocouple for use in a variety of applications;

[0012]FIG. 8 is partially cut-away view of a containment chamberutilized with the thermocouple of FIG. 7;

[0013]FIG. 9 is a schematic illustration of the application of anexemplary thermocouple to sense temperature at a variety of locations orpoints within a chamber; and

[0014]FIG. 10 is a schematic illustration showing another exemplaryconfiguration of the thermocouple illustrated in FIG. 9.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0015] Referring generally to FIG. 1, an exemplary thermocouple system20 is illustrated according to one embodiment of the present invention.Thermocouple system 20 comprises a sheath 22 having an enclosed distalend 24 and an opposed end 26 from which a plurality of conductor pairs28 extend. Each conductor pair comprises a pair of conductors ofdissimilar materials, typically metals, that are joined at a junctionpoint 30. For example, the dissimilar conductors may be welded togetherto form the junction. The free ends of the conductor pairs 28 areconnected to instrumentation 32, e.g. a voltmeter, that measures thedifference in potential created at the junction of the two metals. Thisdifference in potential corresponds to a given temperature.

[0016] Sheath 22 typically comprises an open interior 34 into whichconductor pairs 28 extend. Within interior 34, an insulation material36, such as an electrical insulation material, is disposed about theindividual conductors of conductor pairs 28. In the illustratedembodiment, insulation material 36 generally fills interior 34 aboutconductor pairs 28. Although various electrical insulation materials maybe used, an exemplary material comprises magnesium oxide (MgO).

[0017] As illustrated best in FIG. 2, temperature may be determined at aplurality of locations along the length of sheath 22 by forming junctionpoints at selected locations along the sheath. By way of example, theembodiment of FIG. 2 illustrates four conductor pairs 28A, 28B, 28C and28D each having its own unique junction point 30A, 30B, 30C and 30D,respectively. The junction points 30A-30D are formed at uniquelongitudinal locations along sheath 22 to permit the sensing oftemperature at those unique locations. It should be noted that fourconductor pairs are illustrated for purposes of explanation and thatvarious numbers of conductor pairs can be utilized. For example, twoconductor pairs, three conductor pairs or even up to ten conductor pairsor more can be utilized within sheath 22 depending on space constraintsand the desired application.

[0018] Each conductor pair comprises a first conductor 38 illustrated insolid line and a second conductor 40 illustrated in dashed line in FIG.2. The first conductor 38 and the second conductor 40 of each conductorpair 28 are made of dissimilar conductive materials. Typically, thethermocouple calibration or type is established by the National Bureauof Standards, e.g. J, K, T, E, R or S. The various types typicallyutilize pairs of dissimilar metallic materials. The following chartprovides some examples: Thermocouple Material Thermocouple B&SRecommended Temperature w/Identifying Characteristics Calibration WireGauge Limits F Positive Negative Type J  8 ga. (.128″)   0 to 1400 IronConstantan ™ 14 ga. (.064″)   0 to 1100 (Magnetic) 20 ga. (.032″)  0 to900 24 ga. (.020″)  0 to 700 Type K  8 ga. (.128″)   0 to 2300 Chromel ™Alumel ™ 14 ga. (.064″)   0 to 2000 (Magnetic) 20 ga. (.032″)   0 to1800 24 ga. (.020″)   0 to 1600 Type T 14 ga. (.064″) −300 to +700Copper Constantan ™ 20 ga. (.032″) −300 to +500 (Copper Color) 24 ga.(.020″) −300 to +400 Type E  8 ga. (.128″)  −300 to +1600 Chromel ™Constantan ™ 14 ga. (.064″)  −300 to +1400 (Silver Color) 20 ga. (.032″) −300 to +1200 Type R or 24 ga. (.020″) to 2700 Platinum 13 Rh PlatinumType s Platnum 10 Rh Platnum (Softer than Pt Rh)

[0019] Additionally, various combinations of different conductor pairtypes can be utilized within a single sheath 22. A variety of materialsalso may be used to form sheath 22. For example, stainless steel andInconel™ are appropriate for use in a variety of applications.

[0020] Although a variety of techniques may be used to join thedissimilar conductors at desired junction points 30 within sheath 22,one technique is to provide conductor pairs 28 by forming a plurality ofrods 42 that extend into sheath 22 to distal end 24, as furtherillustrated in FIGS. 3 and 4. The rods 42 are preformed of the materialof first conductor 38, second conductor 40 or a combination of the two.In FIG. 2, for example, four rods 42 are formed of the material ofsecond conductor 40, one rod is formed of the first conductor material38 and three rods are formed of a combination of first conductormaterial and second conductor material that are joined at the desiredjunction point, e.g. 30B, 30C and 30D. When the rods are placed withinsheath 22, the junction points 30A-30D are disposed at desired locationsfor sensing temperature.

[0021] Each of the rods 42 has a distal rod end 44, and the appropriatepairs of rod ends are joined together to form conductor pairs 28, asbest illustrated in FIGS. 3 and 4. Although distal rod ends 44 may bejoined in a variety of ways, the distal rod ends may be fused, e.g.welded, together at a fusion end 46. Alternatively, a cross piece orcross rod may be utilized. For example, a cross piece formed of theappropriate conductor material may be welded or otherwise joined tocorresponding rod ends. When joined, at least some of the conductorscomprise a return segment 47 (see FIG. 2) that returns the conductorfrom the distal end to a junction point 30, e.g. 30B, 30C, 30D, withinsheath 22.

[0022] Although various processes may be used to form thermocouplesystem 20, one exemplary methodology comprises preparing those rods 42with two dissimilar materials by, for example, welding the dissimilarconducting materials together at predetermined points. The combinationrods 42 along with the remaining rods 42 are then passed throughinsulation 36 within the open ended sheath 22 (see FIG. 3). Insulation36 may initially be placed within sheath 22 in the form of beads. Sheath22 is then swaged to compact the insulation 36 and sheath 22.

[0023] Following swaging, the insulation, e.g. MgO, is removed at distalend 24 and the appropriate rods are coupled to form conductor pairs 28,as best illustrated in FIG. 4. For example, cross pieces 46 may bewelded across appropriate rod ends 44. An appropriate insulationmaterial, such as magnesium oxide powder, is placed around theprotruding rod ends (see FIG. 2) and a sheath cap 48 is attached to theremainder of the sheath by, for example, welding.

[0024] Thermocouple system 20 is readily designed for a variety ofapplications. For example, one exemplary application utilizesthermocouple system 20 for sensing temperature at a plurality oflocations within an enclosed environment, such as a tank. In theembodiment illustrated in FIG. 5, the thermocouple system furthercomprises a mounting system 50 designed for attachment to acorresponding flange of a tank (described more fully below). Mountingsystem 50 comprises a plate 52 having a plurality of apertures 54utilized in fastening plate 52 to the corresponding flange by, forexample, threaded fasteners. Mounting system 50 further includes anopening or openings 56 through which sheath 22 passes into thecontainer. Sheath 22 is sealed to plate 52 at its corresponding opening56 by, for instance, a socket weld 58.

[0025] In the illustrated embodiment, a containment chamber 60 is formedby a containment wall 62 connected to a back surface 64 of plate 52.Containment wall 62 is connected to plate 52 by, for example, a weld 66.At an end opposite plate 52, containment chamber 60 is enclosed by aplate 68 having one or more plate openings 70 through which one or moresheaths 22 extend. Each sheath is sealed within its correspondingopening 70 by, for example, a socket weld 72.

[0026] Containment wall 62 also may include one or more openings 74 thatprovide selective access to the containment chamber. For example, in theillustrated embodiment, a pair of bosses 76 are attached to an exteriorsurface 78 of containment wall 62 proximate openings 74. The bosses 76may be attached to containment wall 62 by appropriate welds 80.

[0027] Each boss 76 is designed to receive an appropriate instrument,e.g. a valve 82. In the illustrated embodiment, one of the valves 82 iscoupled to a T-section 84 which, in turn, is coupled to a pressure gauge86 and an additional valve 88. In this exemplary embodiment, thepressure gauge 86 is attached to determine whether any high pressurefluid leaks into containment chamber 60, as described in more detailbelow. Depending on the application, a variety of instruments may becoupled to containment chamber 60.

[0028] From containment chamber 60, sheath 22 extends through a supportbracket 90 to which it is attached by appropriate fasteners 92, e.g. abulk head connector. Subsequent to fastener 92, sheath 22 extends to ajunction box 94 having a terminal block 96. The various conductor pairs28 are coupled to appropriate terminals 98 of terminal block 96. Theterminal block may be connected to appropriate instrumentation, such asinstrumentation 32, to determine the various potential differences, andthereby the temperatures, at each of the junction points 30.

[0029] Referring generally to FIGS. 6 and 7, a specific application ofan alternate thermocouple system is illustrated. In this embodiment, ahigh pressure chemical reaction vessel 100 is designed for a desiredchemical process. For example, high pressure vessel 100 may be utilizedin the petroleum industry and may comprise a hydrocracker, ahydrotreater, a hydrogen reactor, a catalytic reactor, a catalyticcracker or an ethylene oxide reactor. Vessel 100 also may be utilizedwith weld pad or tube skin applications. In an exemplary application,one or more high pressure chemical reaction vessels 100 are coupled to amanifold pipe 102 by a connector pipe 104. Connector pipe 104 isdisposed in fluid communication with the interior of vessel 100generally at an upper portion 105 of vessel 100. Similarly, a secondmanifold pipe 106 is coupled to the one or more vessels 100 by anappropriate lower connector pipe 108. Lower connector pipe 108 generallyis connected in fluid communication with vessel 100 at a lower or bottomportion 110. Manifold pipe 102 and second manifold pipe 106 can be usedto provide ingress or egress of fluids moving to or from high pressurechemical reaction vessel or vessels 100.

[0030] In a petrochemical application, petrochemicals move into highpressure chemical reaction vessels 100 in either direction depending onthe specific application. For example, flow can be from manifold pipe102 downward through vessel 100 and out through second manifold pipe106. Alternatively, the flow can be in the reverse direction moving fromsecond manifold pipe 106 upwardly through vessels 100 to manifold pipe102.

[0031] Typically, one or more beds 112 are deployed within high pressurechemical reaction vessel 100 at various levels. The number and type ofbeds vary according to the environment and the types of high pressureand high temperature reactions that take place within the reactor, e.g.high pressure chemical reaction vessel 100, for a given application. Tosense the reaction temperature at different levels and to control theproper reaction rate, temperature is sensed at various selected levelswithin vessel 100.

[0032] One or more thermocouple systems 20 are deployed to extenddownwardly into the interior of vessel 100 for sensing temperature at aplurality of longitudinal locations within the pressure vessel. Itshould be noted that one or more systems 20 also can be deployed fromthe side (e.g. horizontally) and/or from the bottom of vessel 100. Asdescribed above, sheath 22 encloses a plurality of conductor pairs 28designed to sense temperature at a plurality of unique, longitudinalpositions along the sheath. However, additional sheaths can be designedto extend into pressure vessel 100 to provide an even greater number ofsensing points for detecting temperature within vessel 100. For example,the embodiment illustrated best in FIG. 7 shows four sheaths extendingdownwardly from mounting plate 52. Each sheath 22 may enclose aplurality of conductor pairs 28, as described with reference to FIGS.1-4.

[0033] The use of multiple thermocouples in each sheath facilitates theuse of numerous thermocouples with a minimal number of welds at mountingplate/flange 52. For example, the embodiment illustrated in FIG. 7 onlyrequires four welds about the four sheaths 22, while multiplethermocouples may be deployed in each sheath. This is advantageous overprior art designs where each thermocouple had its own sheath requiring aseparate weld. In many such applications, the relatively large number ofwelds could not be accommodated at the flange.

[0034] The number of conductor pairs 28 within each sheath and thenumber of sheaths utilized can be adjusted according to application anddesign parameters. For example, a single sheath may be able to containsufficient conductor pairs 28 to provide temperature sensing capabilityat all of the desired locations, or the temperature sensing junctionscan be divided between additional sheaths. Also, the use of additionalsheaths that each contain one or more conductor pairs 28 permits thosesheaths to be bent, curled, arced or otherwise formed to sensetemperatures at a variety of other locations within the vessel 100.

[0035] As illustrated best in FIG. 8, the one or more sheaths 22preferably include a relief section 114 disposed within containmentchamber 60 to facilitate flexing of the sheath due to, for example,thermal expansion. The relief section 114 of each sheath may comprise anarcuate section 116 that provides the sheath with sufficientflexibility.

[0036] Depending on the application and type of vessel 100 utilized inthe application, the attachment of thermocouple system 20 to pressurevessel 100 may vary. However, one exemplary embodiment utilizes a neck118 fastened to vessel 100 by, for example, a weldment. Neck 118 isdeployed around an opening 120 formed through the outer wall 122 ofvessel 100. A flange 124 is connected to an upper end of neck 118 tofacilitate mounting of thermocouple system 20. Flange 124 typically iswelded to neck 118. If additional thermocouple systems 20 are utilizedfor a given application, a plurality of necks and flanges may be coupledto the pressure vessel as described.

[0037] Flange 124 may include a plurality of apertures 126 configuredfor alignment with apertures 54 of mounting plate 52. Appropriatefasteners 128, such as bolts, can be inserted through apertures 54 and126 to secure each thermocouple system 20 to the appropriate highpressure chemical reaction vessel 100. As illustrated, the sheath orsheaths 22 simply are inserted into the interior of vessel 100 via neck118, and plate 52 is secured to flange 124. Additionally, appropriateseals can be utilized intermediate flange 124 and plate 52 to preventescape of high pressure fluids, depending on a particular application,and as known to those of ordinary skill in the art. It should be notedthat numerous types of flanges and other connectors can be utilized incoupling each thermocouple system 20 to a given high pressure chemicalreaction vessel.

[0038] The use of multiple conductor pairs able to sense temperature ata plurality of unique locations within a single sheath permits greatflexibility in the design of the thermocouple. For example, the sheathmay be formed along a contour 130, as illustrated in FIG. 9. Themultiple conductor pairs 28 having junction points 30 separatedlongitudinally along the sheath 22 permits detection of temperature at aplurality of unique locations 132 along contour 130. Thus, thetemperature detection points are not necessarily disposed linearly alonga relatively straight sheath.

[0039] The contour 130 illustrated in FIG. 9 is formed as an arc,however, contour 130 may comprise a variety of other shapes andarrangements. For example, the embodiment of FIG. 10 utilizes a sheaththat is bent downwardly along a relatively straight contour 134 beforetransitioning into an arced contour 136. Contour 136 is deployedgenerally along the arcuate outer wall of a vessel 138, as illustratedin both FIGS. 9 and 10.

[0040] It will be understood that the foregoing description is ofexemplary embodiments of this invention, and that the invention is notlimited to the specific forms shown. For example, the materials utilizedin forming the thermocouples may be adjusted according to changes inthermocouple design, advancement of material science, the environment ofuse, etc. Additionally, the multipoint thermocouples described can beutilized in a variety of applications that may require various mountingstructures, support structures and instrumentation. Various applicationsmay or may not require containment chambers, and a variety of vesselsranging from low pressure vessels to high pressure vessels may beutilized for the reaction and/or flow of a variety of substances. Theseand other modifications may be made in the design and arrangement of theelements without departing from the scope of the invention as expressedin the appended claims.

What is claimed is:
 1. A multipoint thermocouple system, comprising: asheath; a plurality of conductor pairs, each conductor pair having twoconductors of dissimilar materials joined at a junction point, thejunction points being disposed at separate longitudinal locations withinthe sheath; and an electrical insulation material disposed about andextending between the plurality of conductor pairs within the sheath. 2.The multipoint thermocouple system as recited in claim 1, wherein theplurality of conductor pairs comprises at least two conductor pairs. 3.The multipoint thermocouple system as recited in claim 1, wherein theplurality of conductor pairs comprises at least three conductor pairs.4. The multipoint thermocouple system as recited in claim 1, wherein theplurality of conductor pairs comprises at least four conductor pairs. 5.The multipoint thermocouple system as recited in claim 1, wherein theplurality of conductor pairs comprises at least ten conductor pairs. 6.The multipoint thermocouple system as recited in claim 1, wherein theelectrical insulation material comprises magnesium oxide.
 7. Themultipoint thermocouple system as recited in claim 1, wherein the sheathcomprises a metallic material.
 8. The multipoint thermocouple system asrecited in claim 1, wherein the sheath is generally linear.
 9. Themultipoint thermocouple system as recited in claim 1, wherein the sheathat least partially extends in an arc.
 10. A temperature sensing device,comprising: a sheath having an insulating material disposed therein; aplurality of first conductors; and a plurality of second conductors, thesecond conductors being formed of a different material than the firstconductors, the first conductors being connected to corresponding secondconductors within the insulating material at a plurality of uniquelongitudinal locations, wherein the insulating material fills theinterstices between the plurality of first conductors and secondconductors.
 11. The temperature sensing device as recited in claim 10,wherein each of the plurality of first conductors comprises a rod thatextends substantially along the length of the sheath.
 12. Thetemperature sensing device as recited in claim 10, wherein theinsulating material comprises magnesium oxide.
 13. The temperaturesensing device as recited in claim 10, wherein the sheath comprises ametal material.
 14. The temperature sensing device as recited in claim10, wherein the plurality of first conductors each comprise a type Jmaterial.
 15. The temperature sensing device as recited in claim 10,wherein the plurality of first conductors each comprise a type Kmaterial.
 16. The temperature sensing device as recited in claim 10,wherein the plurality of first conductors each comprise a type Tmaterial.
 17. The temperature sensing device as recited in claim 10,wherein the plurality of first conductors each comprise a type Rmaterial.
 18. The temperature sensing device as recited in claim 10,wherein the plurality of second conductors each comprise a type Ematerial.
 19. The temperature sensing device as recited in claim 10,wherein the plurality of second conductors each comprise a type Kmaterial.
 20. The temperature sensing device as recited in claim 10,wherein the plurality of second conductors each comprise a type Smaterial.
 21. A method of forming a multipoint thermocouple, comprising:connecting a first pair of dissimilar conductors at a first longitudinalposition; connecting a second pair of dissimilar conductors at a secondlongitudinal position; and enclosing the first pair and the second pairwith a single sheath.
 22. The method as recited in claim 21, furthercomprising surrounding the first pair and the second pair with aninsulating material.
 23. The method as recited in claim 22, furthercomprising connecting a third pair of dissimilar conductors at a thirdlongitudinal position within the sheath.
 24. The method as recited inclaim 21, wherein connecting the second pair comprises forming one ofthe dissimilar conductors of the second pair with a return segment. 25.The method as recited in claim 21, wherein connecting the second paircomprises; forming the second pair with a first rod and a second rodthat extend at least substantially through the sheath; and couplingtogether the first rod and the second rod at a distal end.
 26. Themethod as recited in claim 21, further comprising bending the sheath toa desired shape.
 27. A method of forming a temperature sensing device,comprising: forming a first conductor rod of a first material; forming asecond conductor rod of a first section of the first material and asecond section of a second material joined at a junction point; placingan insulation material within a sheath; deploying the first and secondconductor rods within the sheath; and connecting the first conductor rodto the first section of the second conductor rod.
 28. The method asrecited in claim 27, wherein connecting comprises connecting the firstand second conductor rods proximate a distal end of the sheath.
 29. Themethod as recited in claim 28, further comprising swaging the sheath.30. The method as recited in claim 29, further comprising enclosing thedistal end with a sheath tip.
 31. The method as recited in claim 30,wherein connecting the first and second conductor rods compriseswelding.